Living Longer

The dramatic increase in average life expectancy during the 20th century ranks as one of society’s greatest achievements. Although most babies born in 1900 did not live past age 50, life expectancy at birth now exceeds 83 years in Japan—the current leader—and is at least 81 years in several other countries. Less developed regions of the world have experienced a steady increase in life expectancy since World War II, although not all regions have shared in these improvements. (One notable exception is the fall in life expectancy in many parts of Africa because of deaths caused by the HIV/AIDS epidemic.) The most dramatic and rapid gains have occurred in East Asia, where life expectancy at birth increased from less than 45 years in 1950 to more than 74 years today.

These improvements are part of a major transition in human health spreading around the globe at different rates and along different pathways. This transition encompasses a broad set of changes that include a decline from high to low fertility; a steady increase in life expectancy at birth and at older ages; and a shift in the leading causes of death and illness from infectious and parasitic diseases to noncommunicable diseases and chronicconditions.

In early nonindustrial societies, the risk of death was high at every age, and only a small proportion of people reached old age. In modern soieties, most people live past middle age, and deaths are highly concentrated at older ages.

The victories against infectious and parasitic diseases are a triumph for public health projects of the 20th century, which immunized millions of people against smallpox, polio, and major childhood killers like measles. Even earlier, better living standards, especially more nutritious diets and cleaner drinking water, began to reduce serious infections and prevent deaths among children. More children were surviving their vulnerable early years and reaching adulthood. In fact, more than 60 percent of the improvement in female life expectancy at birth in developed countries between 1850 and 1900 occurred because more children were living to age 15, not because more adults were reaching old age. It wasn’t until the 20th century that mortality rates began to decline within the older ages. Research for more recent periods shows a surprising and continuing improvement in life expectancy among those aged 80 or above.

The progressive increase in survival in these oldest age groups was not anticipated by demographers, and it raises questions about how high the average life expectancy can realistically rise and about the potential length of the human lifespan. While some experts assume that life expectancy must be approaching an upper limit, data on life expectancies between 1840 and 2007 show a steady increase averaging about three months of life per year. The country with the highest average life expectancy has varied over time (Figure 4). In 1840 it was Sweden and today it is Japan—but the pattern is strikingly similar. So far there is little evidence that life expectancy has stopped rising even in Japan.